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Nightingale B, Dersch CM, Boos TL, Greiner E, Calhoun WJ, Jacobson AE, Rice KC, Rothman RB: Studies of the biogenic amine transporters. J Pharmacol Exp Ther. 2005 Aug;314(2):906-15. Epub 2005 Apr 28.
XI. Identification of a 1-[2-[bis (4-fluorophenyl) methoxy] ethyl]-4-(3-phenylpropyl) piperazine (GBR12909) analog that allosterically modulates the serotonin transporter.. Previous studies identified partial inhibitors of serotonin (5-HT) transporter and dopamine transporter binding. We report here on a partial inhibitor of 5-HT transporter (SERT) binding identified among a group of 1-[2-[bis (4-fluorophenyl) methoxy] ethyl]-4-(3-phenylpropyl) piperazine analogs (4-[2-[bis (4-fluorophenyl)-methoxy] ethyl]-1-(2-trifluoromethyl-benzyl)-pip eridine; TB-1-099). Membranes were prepared from rat brains or human embryonic kidney cells expressing the cloned human dopamine (hDAT), serotonin (hSERT), and norepinephrine (hNET) transporters. beta-(4'-(125) Iodophenyl) tropan-2beta-carboxylic acid methyl ester ([(125) I] RTI-55) binding and other assays followed published procedures. Using rat brain membranes, TB-1-099 weakly inhibited DAT binding (K (i) = 439 nM), was inactive at NET binding ([(3) H] nisoxetine), and partially inhibited SERT binding with an extrapolated plateau ("A" value) of 20%. Similarly, TB-1-099 partially inhibited [(125) I] RTI-55 binding to hSERT with an extrapolated plateau (A value) of 14%. Upon examining the effect of increasing concentrations of TB-1-099 on the apparent K (d) and B (max) of [(125) I] RTI-55 binding to hSERT, we found that TB-1-099 decreased the B (max) in a dose-dependent manner and affected the apparent K (d) in a manner well described by a sigmoid dose-response curve. TB-1-099 increased the K (d) but not to the magnitude expected for a competitive inhibitor. In rat brain synaptosomes, TB-1-099 noncompetitively inhibited [(3) H] 5-HT, but not [(3) H] dopamine, uptake. Dissociation experiments indicated that TB-1-099 promoted the rapid dissociation of a small component of [(125) I] RTI-55 binding to hSERT. Association experiments demonstrated that TB-1-099 slowed [(125) I] RTI-55 binding to hSERT in a manner unlike that of the competitive inhibitor indatraline. Viewed collectively, these results support the hypothesis that TB-1-099 allosterically modulates hSERT binding and function. |
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